There are many types of thinset; primarily modified and unmodified. An unmodified is also called a dryset thinset (mortar).
A thinset is typically spec'ed for a maximum of 1/4" thick application layer. If you need more than that in one layer, you'd use a medium bed mortar (often called granite or marble motar). Depending on the formulation, these can ususually be installed up to around 1/2" thick, and have more sand in them to support big tiles (not that thinset can't be used for big tiles - depends on how flat the floor and tile are and other considerations).
With a modified thinset, it needs to both cure (chemical reaction with the cement and water) AND dry out. One of the primary things in a modified thinset is a laytex or similar compound. This needs to dry out.
Mixing a thinset must be done to the manufacturer's specs - in essence, on a modified thinset you need to first wet all of the components, let it slake (rest), then mix again to then cover all of the mortar cement bits with laytex that was hydrated in the first action. If you don't do that, it won't have the proper consistency nor will it have the stated strength. This will have a HUGE difference when it comes time to use it.
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